I have a comment on #3, regarding safety. If you try to stop the technique, the other person may react by ramping up power or changing suddenly, either of which can be dangerous
I've backed off from doing this too much as I have gotten older, but in the past people have been hurt and broken when they tried that crap on me. If I feel a change to what I am just trying to show -I will change with them and continue.
Sometimes it's a new student not understading the danger inherently involved. Most of the time the smartalec who pulled that kind of crap was simply not as prepared for the outcome. It has precedent with some very famous Budo teachers. Teaching a waza is not to be confused with fighting and positional change. Only a fool would do it more than once.
Often the teacher is teaching with more respect for the student than that very student is aware of.